German reference DE-A1-30 09 279 discloses a synchronous machine having a stator with permanent magnets for the excitation, leaving more space providing the power windings than in the case where windings are used as the excitation. The permanent magnets are located around the stator side of the device. Further, a toothed laminated rotor is arranged inside the stator's inner circumference.
In this configuration known from the above German reference, the permanent magnets are utilized for operational excitation. In this manner of using the permanent magnets, one no longer needs an excitation winding. Thus, extra space is gained for the power windings and/or the machine weight can be economized for a synchronous machine provided as a generator. An embodiment of the German reference, however, has the permanent magnets partially replaced by exciting windings. The magnetic fields of the permanent magnets and the exciting windings work separately.
A heteropolar generator with a stator having the stator subdivided into stator sectors is also known from DE 3050269. With this type of stator, only the excitation windings are providing the excitation; they are wound around the stator yoke; permanent magnets are not used.
There is therefore needed a synchronous machine in which the electric excitation means on the stator is reduced, while maintaining or even reducing the size of the motor and preserving all advantages of an electric excitation system.